Triplanar knee resection method

ABSTRACT

An improved triplanar knee resection system is provided for preparing a knee joint for a prosthesis. The apparatus of the triplanar knee system includes a single guide member for use in resecting the distal femoral condyles, the proximal tibia, and the distal femur. The guide member cooperates with a simplified set of instruments, including femur and tibia guide rods, a tibia adaptor, a tibia bar, and a femur bar, for establishing equal flexion and extension gaps and triplanar resections. The method of the triplanar knee system provides a simplified procedure for use by an orthopedic surgeon in properly preparing a knee joint for implantation of a prosthesis.

BACKGROUND

The invention relates generally to knee surgical techniques and, moreparticularly, to apparatus and method for resection of the knee jointfor a knee prosthesis.

Replacement of a knee joint with a prosthesis involves a comprehensivesurgical procedure, as is known to those skilled in the art. Thesurgical procedure is complicated by the fact that only a relativelysmall area of the patient's leg, namely the knee, is exposed during theoperation. The remainder of the patient's leg, as well as most of hisbody, is covered with sterile drapes. The R.M.C.™ Total Knee Systemtechnique manual published by Richards Manufacturing Company, Inc., 1450Brooks Road, Memphis, Tenn. 38116 illustrates this aspect of thesurgical procedure. The surgical procedure is further complicated by thepresence of the muscle and skin tissue which surrounds the knee joint.

Once the knee joint is exposed by known techniques, the distal femur andproximal tibia must be prepared to enable implantation of theprosthesis. Such preparation includes resection of the anterior andposterior distal femoral condyles, the proximal tibia, and the distalfemur. In order to achieve proper stability of the knee prosthesis whenimplanted, the aforementioned resections must be accurately alignedrelative to an imaginary axis extending through the hip joint, kneejoint, and ankle joint.

It is necessary for the distal femoral condylar resections to beparallel to the proximal tibial resection when the knee is in flexionand for the proximal tibial resection when the knee is in extension.These "triplanar" resections should be made to provide equal flexion andextension gaps, i.e., the distance between the posterior femoralcondylar resection and the proximal tibial resection with the knee inflexion (the flexion gap) should be equal to the distance between thedistal femoral resection and the proximal tibial resection with the kneein extension (the extension gap). Furthermore, the resected proximaltibia and resected distal femur should be perpendicular to theabove-referenced imaginary axis when the knee is extended.

The necessity of accurately making the triplanar resections has led tothe development of relatively complicated instrumentation to aid theorthopedic surgeon. Illustrative of such instrumentation are theHowmedica® Universal™ Total Knee Instrument System as shown in thecatalogue published by Howmedica, Inc., Orthopaedics Division, 359Veterans Blvd., Rutherford, N.J. 07070 and the Insall/Burstein surgicalinstrument system as designed by John Insall, M.D. and Albert H.Burstein, Ph.D. and shown in the publication entitled "Knee ReplacementUsing the Insall/Burstein Total Condylar Knee System."

Although providing some guidance to the orthopedic surgeon, these priorinstrument systems utilize long alignment rods which have proved to beless than satisfactory under sterile operating room conditions, asdescribed previously. Furthermore, such instrument systems includenumerous components which still require much manual manipulation andwhich are cumbersome to use.

SUMMARY

In accordance with the present invention, an improved triplanar kneeresection system, free of many disadvantages of the prior art, isprovided. The triplanar knee system includes a single guide member foruse in making the proper bone resections. The guide member includes analignment opening for cooperating with a guide rod. The guide rod has a90° angle bend and is adapted to be inserted into the femur for use inaligning the guide member. In one aspect of the present invention, theguide rod is designed such that it remains inserted in the femur duringthe surgical procedure, thereby establishing a common reference pointfor the bone resections.

The guide member includes three pairs of parallel guide slots which areutilized in making the triplanar bone resections. The guide membercooperates with the guide rod to enable resection of the knee joint withthe knee always in flexion.

A second identical guide rod is provided along with a tibia adapter anda tibia bar for use with the guide member in resecting the proximaltibia. A femur bar is provided for use with the guide member and femurguide rod in making the resection of the distal femur.

In a second aspect of the present invention, the femur guide bar isdesigned to compensate for the appropriate valgus angle of the femurrelative to an imaginary axis extending through the hip joint, kneejoint, and ankle joint. In another aspect of the present invention, thetriplanar knee system achieves equal flexion and extension gaps of theresected knee joint. In still another aspect, the triplanar knee systemensures proper alignment of the distal femoral resection and theproximal tibial resection although these two resections areindependently aligned.

In a method aspect of the invention, a common reference is establishedfor resecting the anterior and posterior distal femoral condyles and thedistal femur. This common reference is used to provide equal flexion andextension gaps.

In another aspect of the method, the alignment of the guide member forresecting the distal femur is accomplished without the use of any"eyeball" techniques.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other advantages and features of the present invention willbecome apparent from the following detailed description considered inconnection with the appended drawings in which like parts are givenidentical reference numerals and in which:

FIG. 1A is an illustrative view of a triplanar guide member cooperatingwith a guide rod for making the distal femoral condylar resections inaccordance with the present invention;

FIG. 1B is an illustrative view, partially cut away for detail, of therear side of the triplanar guide member of FIG. 1A;

FIG. 2A is a side view of the guide member cooperating with a secondguide rod, a tibia adaptor, and a tibia bar for resecting the proximaltibia in accordance with the present invention;

FIG. 2B is an illustrative view of the tibia adaptor of FIG. 2A;

FIG. 2C is an illustrative view of the tibia bar of FIG. 2A;

FIG. 2D is a cross section of the tibia guide rod taken along sectionline 2D--2D in FIG. 2A;

FIG. 2E is an illustrative view of the rear side of the triplanar guidemember of FIG. 2A, partially cut away for detail;

FIG. 3 is an illustrative view of the femoral guide rod being used todetermine the flexion gap in accordance with the present invention;

FIG. 4 is a top view of the femoral guide member being used to establishan extension gap equal to the flexion gap in accordance with the presentinvention;

FIG. 5A is a top view of the guide member cooperating with the femoralguide rod and a femur bar for proper positioning of the guide memberwith the knee extended in accordance with the present invention;

FIG. 5B is an illustrative view of the femur bar of FIG. 5A;

FIG. 6 is a side view of the guide member cooperating with the femoralguide rod and femur bar with the knee in flexion in accordance with thepresent invention;

FIG. 7A is an illustrative view of a modified femur bar;

FIG. 7B is an illustrative view of a pointer for use with the modifiedfemur bar of FIG. 7A;

FIG. 7C is a schematic diagram of the modified femur bar cooperatingwith the pointer and the guide member to establish the proper valgusangle in accordance with the present invention; and

FIG. 8 is an illustrative view of a modified tibia bar for use with thepointer of FIG. 7B.

DETAILED DESCRIPTION

Referring now to FIGS. 1A and 1B, shown is a knee joint 20 including adistal femur 22 and proximal tibia 24 in flexion. It is to be understoodthat the exposure of the distal femur and proximal tibia is achieved byknown surgical techniques. Such known techniques may include removal ofthe anterior and posterior cruciate ligaments (not shown). However, thepresent invention is applicable in making bone resections for a cruciatesparing prosthesis as well.

A pair of collateral ligaments 26, which connect the distal femur 22 andproximal tibia 24, are left in place. It is to be understood that anynecessary ligamentous release may be preformed by known surgicaltechniques before making the appropriate bone resections for replacementof the knee.

In accordance with the present invention, with the knee in flexion, afirst hole 28 is drilled into the end of distal femur 22, approximatelycentered in the medullary canal by known techniques. Likewise, a secondhole 30 is drilled into the end of proximal tibia 24, slightly anteriorrelative to the centerline extending into the medullary canal of thetibia.

A femur guide rod 32 having a longer portion 34 and a shorter, threadedportion 35 forming an L-shaped is inserted into a triplanar guide member36. Guide member 36 has a generally rectangular configuration with afront surface 38, a rear surface 40, a top surface 42, a bottom surface44, a left surface 46, and a right surface 48. Guide member 36 includesthree pairs of resection guide slots 50, 52, 54 which are utilized tomake the appropriate bone resections. A vertical guide slot 56 iscentrally located in the guide member relative to sides 46, 48. Guideslot 56 forms a guide rod recess 58 at its upper end. A vertical bore 60extends upward from guide rod recess 58 through guide member 36. Guiderod recess 58 and bore 60 are configured to matingly receive threadedportion 35 of guide rod 32 and to stabilize the guide rod with respectto guide member 36. The guide rod is secured in place with a circularnut or cap 62, which is threaded onto threaded portion 35 of the guiderod until the nut or cap abuts top surface 42 of guide member 36.

Guide member 36 may be provided with a pair of handles 64. It is to beunderstood that handles 64 may be integrally formed with guide member 36or may be threadably connected to the guide member and still remainwithin the contemplation of the present invention. Guide member 36 isalso provided with a plurality of pins 66 protruding outwardly from rearside 40. Pins 66 are adapted to anchor the guide member into the bone toprevent the guide member from rotating during use.

As shown in FIG. 1A, femur guide rod 32 is inserted into drilled hole28. Before pressing pins 66 into the end of distal femur 22, guidemember 36 is manually oriented to obtain the proper alignment of theguide member relative to the anterior and posterior distal femoralcondyles, identified as 68 and 70, respectively, as is known to thoseskilled in the art. When aligned, guide members pins 66 are pressed intothe distal femur. Anterior distal femoral condyles 68 are resected withan oscillating saw (not shown) or the like by using upper guide slots50. Likewise, posterior distal femoral condyles 70 are resected with anoscillating saw with the aid of bottom guide slots 54. The guide memberand guide rod are then pulled partially out to disengage pins 66, andguide member 36 is then removed from guide rod 32 after removing cap 62.Preferably, femur guide rod member 32 is then pushed back into hole 28and remains there for later resection of the distal femur. It is to beunderstood, however, that guide rod 32 may be removed from the femur andreinserted later for use in resecting the distal femur. Any remainingportion of the anterior or posterior distal femoral condyles, such as inthe center region where the guide slots do not extend, may then beremoved by using the previously resected bone portions as a levelingguide.

The proximal tibia is then subluxed to its forward position, as shown inFIG. 2A. A tibia guide rod adapter 72 is slidably disposed onto a longerportion 75 of a second guide rod 73, which is identical to the firstguide rod that remains inserted in the femur during this stage of theprocedure. As shown in FIG. 2B, adapter 72 has an opening 74 whichcooperates with a recess 76 to stabilize guide rod 73 relative to theadapter. Tibia adapter 72 is provided with a pair of pins 78, which arepressed into the end of the proximal tibia to prevent the guide rod fromrotating about the longitudinal axis extending through longer portion75. The guide rod carrying the tibia adapter 72 is inserted into drilledhole 30, and a shorter portion 77 of guide rod 73 is manually orientedsuch that a plane extending through the L-shaped guide rod is parallelto the sagittal plane extending through the tibia. When properlyaligned, the guide rod is pushed further into hole 30, therebyimplanting tibia adapter pins 78 and preventing rotation of guide rod73.

A tibia bar 80 having an extended threaded portion 82 and a generallyrectangular base 84, as shown in FIG. 2C, is inserted into verticalguide slot 56 of guide member 36 such that threaded portion 82 extendsthrough vertical bore 60 in the guide member. A second cap 63 isthreaded partially onto the threaded portion of tibia bar 80. Therectangular base of the tibia bar has a bore 86 extending lengthwisetherethrough, and a key lock 88 protrudes from the bottom center of bore86. The bottom edges of base 84 are slightly chamfered, as shown at 89.Guide member 36 with the tibia bar inserted therein is inverted, and theguide member and tibia bar are inserted onto threaded portion 77 ofguide rod 73. The shorter portion of the guide rod includes a key seat90 (see FIG. 2D) which cooperates with key lock 88 to properly align theguide member 36 for resecting the proximal tibia. FIG. 2E illustratesthe cooperation of guide member 36, tibia bar 80, guide rod 73, andtibia adaptor 72.

In order to properly align the guide member for resection of theproximal tibia, cap 63, threaded onto the threaded portion 82 of tibiabar 80, is either loosened or tightened to lower (by gravity) or raisecenter guide slots 52 of the guide member relative to the proximaltibia. When properly positioned, the guide member and tibia bar arepushed further onto shorter portion 77 of the guide rod, therebyimplanting pins 66 in the anterior side of the proximal tibia. Cap 62,threaded onto shorter portion 77, is then tightened. An oscillating sawis inserted through center slots 52 of the guide member, and theproximal tibia is then resected. Cap 62, threaded onto the guide rod, isthen loosened, guide member pins 66 are disengaged, and guide rod 73supporting the guide member and tibia bar 80 is then removed, along withtibia adapter 72. Any remaining portion of the proximal tibia may thenbe leveled by using the previously resected portions as a levelingguide.

Having now completed two of the triplanar resections, the flexion gapbetween the resected proximal tibia and the resected posterior distalfemur is determined. As shown in FIG. 3, threaded portion 35 of theguide rod 32, which remained inserted in the femur during resection ofthe proximal tibia, is oriented in a direction perpendicular to theresected surface of the proximal tibia. Threaded portion 35 has a flatportion 92 along one side thereof. Flat portion 92 has two sets of marks94, 96 which indicate the relative thicknesses of various tibialcomponents for knee prostheses, such as those manufactured and soldunder the names of Howmedica® Universal™ Total Knee Instrument Systemand Insall/Burstein Total Condylar Knee System. The marks are located atpredetermined positions along the flat portion 92 of the guide rod toindicate the proper tibial component to be utilized in the kneeprosthesis. With collateral ligaments 26 extended taughtly, the flexiongap is determined by verifying which mark is level with the resectedsurface of the proximal tibia. It is to be understood that any set ofmarks corresponding to a particular brand of tibial component may beutilized and still remain within the contemplation of the presentinvention.

Once the flexion gap is determined by selecting the appropriate tibialcomponent mark, the knee is temporarily placed in extension, as shown inFIG. 4. The guide rod is then positioned with shorter portion 35extending upward and perpendicular to resected anterior distal femur 68such that the outer edge of the shorter portion rests upon the resectedproximal tibia when collateral ligaments 26 are extended taughtly.

Referring now to FIGS. 5A and 5B, with the knee in extension, a femurbar 98 having a smooth extended portion 100 and a generally rectangularbase 102 is inserted into guide member 36 such that smooth extension 100extends through vertical bore 60. Base 102 of femur bar 98 has itsbottom edges slightly chamfered as shown at 103, like the chamferededges described in connection with base 84 of tibia bar 80. Femur barbase 102 has a bore 104 extending lengthwise therethrough. A key lock106 protrudes from opening 104 at a position offset 7° from the bottomcenter of the opening. Key lock 106 is offset to compensate for thevalgus angle of the femur. As is known to those skilled in the art, thevalgus angle typically has a magnitude of 5°-8°. However, the valgusangle may be less than 5° or greater than 8°. It is to be understoodthat key lock 106 may be offset from the bottom center of bore 104 byany amount and still remain within the contemplation of the presentinvention. Alternatively, a plurality of femur bars having a key lockoffset at a variety of different angular displacements may be provided.

The positioning of the femur bar in guide member 36 is critical in thatkey lock 106 must be oriented to one side or the other depending uponwhether the left knee or right knee is being resected. When resectingthe right knee, the femur bar is inserted into the guide member suchthat key lock 106 is to the left of center (when viewing the guidemember from the front). When resecting the left knee, the femur bar isinserted into the guide member such that key lock 106 is to the right ofcenter. Thus, the apparatus of the present invention is universallyapplicable regardless of which knee joint is being resected.

With the femur bar properly inserted into guide member 36 and the kneestill in extension with shorter portion 35 positioned in an upwarddirection, the femur bar and guide member inserted thereon are placedonto the guide rod such that bore 104 of femur bar 98 slides ontoshorter portion 35 of the guide rod. Key lock 106 in bore 104 engageskey seat 90 in shorter portion 35 of the guide rod to prevent the guidemember from rotating relative to the longitudinal axis extending throughthe shorter portion of the guide rod.

As shown in FIG. 5A, the guide member is then slidably positioned alongsmooth extension 100 of femur bar 98 until the top edge, identified as107, of base 102 is aligned with the appropriate mark 94, 96, which wasdetermined by verifying the flexion gap. When top edge 107 is properlyaligned, guide member pins 66 are pressed into the anterior distal femurto prevent the guide member from moving. Cap 62 is then threaded tightlyonto threaded portion 35 of guide rod 32.

Referring now to FIG. 6, the knee is once again placed in flexion, andthe guide member is already properly positioned for resecting the distalfemur without the need for any manual alignment. An oscillating saw isinserted into center slots 52 of the guide member, and the distal femuris resected. Cap 62 is then loosened, guide member pins 66 aredisengaged, and the femur guide rod supporting the guide member andfemur bar are then removed. Any remaining portion of the distal femurmay then be removed by using the previously resected portions as aleveling guide.

An important feature of the present invention resides in the fact thatall of the resections are made with the knee in flexion. This reducesthe danger of cutting the popliteal artery. Another important feature ofthe present invention is that the extension gap is in effect measuredfrom the resected proximal tibia (see discussion in connection with FIG.4). However, the alignment of the distal femur resection is made,without any "eyeball" techniques, by using the reference pointestablished by the femur guide rod instead of using the resectedproximal tibia as a reference point.

Still another important feature of the present invention is that overallalignment of the triplanar resections is assured even though they arealigned independently of each other. Furthermore, the simplifiedinstrumentation of the present invention is designed such that theproximal tibial resection and the distal femoral resection areperpendicular to an imaginary axis extending through the hip joint, kneejoint, and ankle joint and such that the distal femoral condylarresections are parallel to said imaginary axis. Yet, these resectionsare made without any direct reference to this imaginary axis.

The method of the present invention also establishes the flexion gapfirst. An extension gap equal to the flexion gap is then established bymeans of the present invention. This method eliminates the possibilitythat the flexion gap will be too small, thereby requiring the distalfemoral condylar resections to be made too deep. It is to be understoodthat "flexion gap" as used herein means the perpendicular distancebetween the resected surface of the proximal tibia and the resectedsurface of the posterior distal femoral condyles when the knee is inflexion. Likewise, "extension gap" as used herein means theperpendicular distance between the resected surface of the proximaltibia and the resected surface of the distal femur when the knee is inextension.

The present invention results in a resected knee joint whereby theproximal tibial resection is parallel to the distal femoral condylarresections when the knee is in flexion and the proximal tibial resectionis parallel to the distal femoral resection when the knee is inextension. As discussed above, the proximal tibial and distal femoralresections are perpendicular to said imaginary axis. These parallel andperpendicular relationships of the resections are what applicant refersto as "triplanar." These triplanar resections are important for stablefunctioning of a knee prosthesis.

In an alternate embodiment of the present invention, a modified femurbar 108, as shown in FIG. 7A, may be provided. The modified femur barhas a smooth extended portion 110 and a generally rectangular base 112,which are similar to those of femur bar 98. A second shorter extendedportion 114 extends from the top of the base 112 and has two key seats116 disposed 180° apart. A bore 118 in base 112 does not have a keylock. Thus, the modified femur bar with the guide member insertedthereon may rotate freely about shorter portion 35 of guide rod 32. Insuch case, key seat 90 of guide rod 32 may be eliminated.

In order to properly align the guide member to compensate for the valgusangle, a pointer 120 is provided as shown in FIG. 7B. The pointerincludes an elongated portion 122 which is affixed to a shorter portion124 extending perpendicular to the elongated portion 122. The shorterportion is affixed to a generally rectangular base 126. Base 126 has abore 128 extending lengthwise therethrough and parallel to elongatedportion 122. Bore 128 has a pair of key locks 130 which are disposed180° apart. Key locks 130 are adapted to cooperate with Key seats 116disposed on shorter extension 114 of modified femur bar 108.

When the guide member and the modified femur bar inserted therein areplaced onto guide rod 32 with the knee in extension, pointer 120 may beslidably disposed onto shorter extension 114 of modified femur bar 108.Before implanting guide member pins 66, the guide member and modifiedfemur bar may be rotated relative to shorter portion 35 of guide rod 32,such that pointer 120 is aligned with the axis extending through the hipjoint, as shown schematically in FIG. 7C. Thus, the modified femur barin cooperation with the pointer enables the guide member to be alignedat the proper valgus angle, regardless of whether the valgus angle is5°, 8°, 12°, or any other angular measurement.

In another embodiment, a modified tibia bar 132 may be provided, asshown in FIG. 8. Modified tibia bar 132 with its threaded extension 133is identical to tibia bar 80, except that the modified tibia bar has ashorter smooth extension portion 134 extending from the top of its base136. Shorter extension 134 has a pair of key seats 138 disposed 180°apart for cooperating with key locks 130 of pointer 120. Also, a bore140 in base 136 is provided without a key lock. With the modified tibiabar inserted into inverted guide member 36 and placed onto threadedportion 77 of guide rod 73 inserted into the tibia, pointer 120 may beplaced onto shorter extension 134 to properly align the guide member,such that the pointer is parallel to the axis extending through theankle joint. Thus, the modified tibia bar in cooperation with thepointer enables the proper alignment of the guide member regardless ofthe shape of the tibia.

As the bone resections are triplanar, as described above, overallalignment of the resected knee joint is ensured even though pointer 120is aligned with only one of the extreme leg joints (the ankle joint whenmaking the proximal tibial resection and the hip joint when making thedistal femoral resection).

The apparatus and method of the present invention provide a simplifiedand improved system for making the triplanar bone resections of the kneejoint. The guide member eliminates the necessity for a different type ofguide component for each triplanar resection, thereby ensuring properalignment of a knee prosthesis with the axis extending through the hipjoint, the knee joint, and the ankle joint. Furthermore, the triplanarknee resection system of the present invention ensures equal flexion andextension gaps while providing for proper valgus alignment.

It is to be understood that the apparatus of the present invention willadmit of other embodiments. The detailed description is given only tofacilitate understanding of the invention by those skilled in the artand should not be construed as limiting the invention.

What is claimed is:
 1. A method for making triplanar bone resections fortotal knee replacement, including the steps of:resecting the proximaltibia such that it is perpendicular to an imaginary axis extendingthrough the ankle joint, knee joint, and hip joint; resecting theanterior and posterior distal femoral condyles such that they areparallel to each other and perpendicular to said axis when the knee isin flexion; determining the flexion gap; inserting an L-shaped femurguide rod into the medullary canal of the femur, the femur guide rodhaving a first portion and a second portion disposed at a right anglewith respect to said first portion, the first portion being inserted insaid canal; placing the knee in extension; partially extending saidguide rod relative to said femur such that the outer surface of thesecond portion abuts the resected proximal tibia; affixing a guidemember having a first planar slot therein onto the second portion ofsaid guide rod such that said slot is disposed perpendicular to thefemoral medullary canal and relative to said canal to compensate for thevalgus angle and such that said slot is spaced from the outer surface ofthe second portion a distance equal to the flexion gap; placing the kneein flexion, while maintaining said guide rod relative to the distalfemur; and resecting the distal femur in reference to said slot whilethe knee is in flexion.
 2. The method of claim 1, wherein said step ofresecting the proximal tibia comprises:inserting an L-shaped tibia guiderod into the medullary canal of the tibia with the knee in flexion, thetibia guide rod having a first portion and a second portion disposed ata right angle therewith, the first portion being inserted in said canal;stabilizing the tibia guide rod such that said rod is substantiallycoplanar with the tibial medullary canal; affixing said guide memberonto the second portion of the tibia guide rod such that said planarslot is disposed perpendicular to the tibial medullary canal; andresecting the proximal tibia in reference to said slot while the knee isin flexion.
 3. The method of claims 1 or 2, wherein said guide memberincludes second and third planar slots therein and wherein said step ofresecting the anterior and posterior distal femoral condylescomprises:affixing said guide member onto the second portion of thefemur guide rod such that said second and third slots are disposedparallel to the femoral medullary canal and perpendicular to the tibialmedullary canal, said second and third slots being parallel to saidfirst slot; and resecting the anterior and posterior distal femoralcondyles in reference to said second and third slots, respectively. 4.The method of claim 3, wherein said step of resecting the anterior andposterior distal femoral condyles is accomplished prior to said step ofresecting the proximal tibia.
 5. The method of claim 3, wherein saidstep of resecting the proximal tibia is accomplished prior to said stepof resecting the anterior and posterior distal femoral condyles.
 6. Themethod of claim 1, wherein said step of resecting the distal femur inreference to said slot is accomplished by resecting said distal femurthrough said slot while the knee is in flexion.
 7. The method of claim1, wherein said L-shaped femur guide rod includes markings on its secondportion for determining the flexion gap, and wherein said guide memberincludes markings corresponding to said markings on said guide rod, andwherein said method further comprises the steps of:orienting saidL-shaped femur guide rod such that said second portion of said guide rodis generally perpendicular to the resected surface of the proximaltibia; determining the flexion gap in response to said marks on saidsecond portion of said guide rod; and positioning said guide memberrelative to said guide rod in response to said marks on said guidemember and said determined flexion gap.
 8. The method of claim 1,wherein said guide member includes an indicator which lies perpendicularto said first planar slot and wherein said step of affixing a guidemember having a first planar slot therein on a second portion of saidguide rod such that said slot is disposed perpendicular to the femoralmedullary canal and relative to said canal to compensate for the valgusangle comprises the step of aligning with the axis extending from theguide member through the hip joint.